Spinning process for artificial filaments



Patented Nov. 6, 1945 SPINNING PROCESS FOR ARTIFICIAL FILAMENTS RayClyde Houtz, Snyder, N. Y., assignor to E. I. du Pont de Nemours &Company, Wilmington, Del., a corporation of Delaware No Drawing.Application March 4, i944,

Serial No. 525,090

1 Claim.

In U. S. Patent No. 2,236,061 (Izard and Kohn) there is disclosed. aprocess of converting aqueous polyvinyl alcohol solution into shapedproducts which comprises shaping the polyvinyl alcohol into the desiredform, thereafter immersing the shaped material in a coagulating bathconsisting of an aqueous solution of an inorganic salt havingsubstantially no oxidizing action such ,as ammonium sulfate, and finallywashing the coagulated material with water to remove the inorganic salttherefrom. While this process results in clear, transparent flexiblestructures which are a marked improvement over the cloudy brittleproducts which are formed when the previous practice of coagulating thepolyvinyl alcohol in a bath of organic water-miscible solvent, such asacetone or alcohol, is followed, still it is not entirely satisfactoryfrom the commercial standpoint for the reason that it is difficult tocompletely remove the inorganic salts from structures formed by thismethod by washing with water unless prolonged washing is resorted to,and if the washing step is of a duration sufiicient to accomplish thedesired complete removal of salts it is generally found that the wateralso exerts an undesirable swelling action on the polyvinyl alcoholstructures. Moreover, the'concentration of inorganic salt in the washwater is so low that recovery of the salt for reuse is prohibitivelyexpensive and the commercial attractiveness of the process furthersulfers as a consequence.

Therefore, an object of this invention, is to provide an improvedexpedient for washing freshly precipitated polyvinyl alcohol structures.

A further object is to provide for the efiicient and harmless removal ofinorganic salts present in j polyvinyl alcohol structures freshlyprecipitated in an aqueous solution of inorganic salt.

' ,A still further object is to wash freshlyprecipitated polyvinylalcohol structures containing inorganic salt in such fashion that thesalt may be easily and economically recovered from the wash liquid forreuse.

' These and other objects will more clearly appear hereinafter.

Unexpectedly, I have found that if, in place of water, an aqueoussolution of an organic oxy compound from the group consisting of ethylalcohol, acetone and dioxane is employed to wash polyvinyl alcoholstructures freshlyprecipitated from an aqueous inorganic salt solutionsuch as aqueous ammonium sulfate, the complete removal of the salt isaccomplished without injurious effeet on the polyvinyl alcoholstructure, and in addition, when the salt dissolved in the mixed solventreaches a certain critical concentration the solvent separates into twolayers, one containing mainly organic oxy compound and water which maybe immediately reused in the preliminary stages of the washing stepwithout further treatment, and the other being a concentrated solutionof the salt in water from which the salt may be easily and economicallyseparated for re-' use in the coagulating bath. The small amount oforganic oxy compound in this aqueous layer can be easily removed byvolatilization and recovered by condensation for reuse.

Accordingly the objects hereinabove stated are realized by my inventionwhich comprises washing precipitated polyvinyl alcohol structurescontaining residual inorganic salt from'the coagulating bath with anaqueous solution of an or ganic oxy compound of the'group consistingofacetone, ethyl alcohol and dioxane, the water and organic oxy compoundbeing so proportioned that the. solution exerts substantially noswelling action on the polyvinyl alcohol structures. The washing iscontinued until the polyvinyl alcohol structure is completely freed fromthe contaminating salt, and thereafter the structure is dried, e. g. ina current of warm air, and/or is further processed as desired.

A preferred Wash solution suitable for the prac-- tice of this inventionconsists of a mixture of In between .i(l--80%'by volume. If solutionscontaining less than 30% acetone are employed, such solutions have atendency to cause swelling of the polyvinyl alcohol, while if theacetone content is over 80%, the coagulating salt, e. g. ammoniumsulfate, is not completely removed. Other solutions which aresatisfactory include ethyl alcohol and water, in which the alcoholcontent is,

at least and dioxane and water in the ratio of three parts of dioxane totwo of water. In

- using the mixed'solvents of this invention, it is important to selectsuch concentrations of woetone,.ethyl alcohol or dioxane in water aswill have no harmful swelling action on the coagulated structure asfilaments, threads, films, etc., of polyvinyl alcohol which areslightlyswollen tend to lose their strength and are therefore oftenrendered useless. This property of polyvinyl alcohol is in markedcontrast to water-sensitive materials such as threads formed fromregenerated cellulose or from cellulose acetate which may be caused toswell slightly without appreciable reduction in tensile strength.

When employing a wash solution consisting of a mixture of acetone andwater, it is desirable to subject the polyvinyl alcohol structure, afterthe inorganic salt has been removed therefrom and before drying, to afinal rinse with an acetonewater mixture comprising a high proportion,e. g. 95%, of acetone. The purpose of this step is to insure in thefinal stages of drying the presence of a relatively high percentage ofacetone in the acetone-water mixture whereby the polyvinyl alcoholstructure will not be exposed for any appreciable length of time to theaction of water alone.

The following examples are given to illustrate specific applications ofthe invention, but they are in nowise to be considered limitativethereof. Parts and percentage compositions are by weight unlessotherwise indicated.

Example I v 40% solution of ammonium sulfate maintained when samples ofthe threads were tested for at a temperature of 52 C. The filaments wereled back and forth over free-running rollers for- .a total bath travelof 200", and were withdrawn from the bath at the rate of 1000" perminute. During coagulation a spinning tension of 52 grams wasmaintained. The wet filaments containing residual ammonium sulfate werecollected on a spinning bobbin, whichat the end of the operation wasremoved, and placed in a bath of 50% acetone and 50% water by volume,and left for a period Of several hours. The bobbin was then removed fromthe bath and further washed by immersing several times in a freshportion of the acetone-watermixture and was given a final rinse of 95%acetone solution in water, following which the filaments were dried onthe bobbin at room temperature. The yarn was transferred to a twistingmachine and given a twist of 3 turns per inch. The twisted yarn had adenier of 335, and the dried thread had a tenacity of 1.11 grams perdenier. The elongation was 29.4%.

- The solution used in the first wash had settled into a bottom layercontaining mainly ammonium sulfate and water and a supernatant layercontaining mainly acetone and water. These layers were easily separated,the aqueous ammonium sulfate solution being retained for use in. thecoagulating bath, and the acetone-water solution being retained forreuse in the. washing of polyvinyl alcohol yarn.

When samples of this yarn were stretched 50% of their original length,they were found to have a tenacity of 1.19 grams per denier, and anelongation of 7.7%.

test was obtained showing that complete removal of the ammo um sulfatehad been obtained in the washing steps.

Example II A 15% solution of polyvinyl alcohol (fully saponifiedpolyvinyl acetate) was prepared at a temperature of 60 C. This solutionwas extruded through a multiple-hole spinneret into a saturated solutionof ammonium sulfate which was maintained at a temperature of 52 C. Thefilaments were led back and forth over a free-running roller for a totalbath travel of 312" at a spinning tension of 0.11 gram per wind-updenier. The wet yarns containing residual ammonium sulfate werecollected on spinning bobbins at the rate of 1000" per minute. Afterspinning the yarn was reeled into skeins from the wet bobbins, and theskeins were immersed in a tension-free condition in a bath of equalparts by volume of acetone and water. During the immersion period theskeins decreased in length by approximately 50%, and at the same timebecame finely crimped and wool-like in appearance. After several hoursthe skeins were removed from the bath, washed free of ammonium sulfateby using a fresh solution of acetone and water, and were given a finalrinse of pure acetone. They were allowed to dry in the air at roomtemperature. The crimp was of a permanent nature and was not removed byprocessing the yarn through the usual textile operations or bystretching. The used wash solution was treated as in Example I.

When samplesof these threads were tested for the presence of solublesulfates a. negative test was obtained.

Example III Threads of polyvinyl alcohol were formed as in Example I. Atthe end of the spinning operation the spinning bobbin was removed andmounted on a pressure-feed washing chuck. The threads werepressure-washed with a solution of dioxane, 60%, and water, 40% byvolume, for a period of 4 hours, and were then dried.

The threads were stretched twice the original length by passing overrolls heated at C. A strong lustrous yarn was obtained which retainedits water-soluble character.

A negative test was obtained when these threads were tested for thepresence of soluble sulfates.

Example IV A 50% solution of polyvinyl alcohol (fully saponifiedpolyvinyl acetate) was prepared at a temperature of 75 C., and to thiswas added Aerosol OT (sodium dioctyl sulfosuccinate) in an amount equalto 0.01% of the solution. This solution was cast on a glass plate, andexcess solution was removed by a doctor knife.

The plate and film were then immersed in a saturated solution of sodiumsulfate maintained at a temperature of 40 C. After a coagulation periodof approximately 5 minutes the plate and.

economic advantage which greatly adds to the I of an inorganic base withan inorganic or low I molecular weight organic acid, such as thosecontaining less than eight carbon atoms. a My invention enables theproduction, in continuous fashion, of many polyvinyl alcohol structuressuch as filaments, yarns, threads, film,

tubes, etc., which are clear, transparent, flexible and relativelystrong, and which retain their commercial attractiveness of theparticular process of preparing polyvinyl alcohol structures with whichthe present process is concerned.

All variations and modifications of the invention described hereinabovefalling within the spirit thereof are intended to be included within thescope of this invention as defined in the appended claim.

I claim:

In the process for manufacturing filaments, yarns, threads, films andlike structures of polyvinyl alcohol wherein an aqueous solution ofpolyvinyl alcohol is coagulated inan aqueous solution of ammoniumsulfate to form a coagulated polyvinyl alcohol structure containingresidual ammonium sulfate, the improved step which comprises washingsaid coagulated polyvinyl alcohol structure substantially free of saidammonium water-solubility unimpaired. Furthermore, the 20 sulfate with asolution consisting of qual par s ready recovery of the coagulatingsalts and organic solvent from the wash liquid presents an by volume ofacetone and water.

RAY CLYDE HOUTZ.

